Recently, in terms of energy saving such as the conservation of fossil fuel and the prevention of global warming such as the suppression of CO2 gas production, it has been demanded to improve the efficiency of a thermal power plant such as efficiency improvement in a steam turbine. One of the effective measures for improving the efficiency of a steam turbine is to increase the size of a steam turbine long blade. In addition, an increase in the size of a steam turbine long blade is also expected to have secondary effects such as shortening the facility construction period, and reducing the resulting cost by decreasing in the number of casings.
A long blade material having excellent mechanical properties and corrosion-resistance is required to improve the reliability of a steam turbine. A precipitation hardening martensitic stainless steel has a large amount of Cr and a small amount of C and thus has excellent corrosion-resistance. However, the balance between the strength and toughness thereof is poor (see, e.g. Japanese patent publication No: 2005-194626).
A material which contains increased amounts of precipitate forming elements to increase strength has a low martensite transformation finish-temperature (martensite transformation finish point), leading to problems with productivity. For example, a sub-zero treatment cooling with dry ice, is required to obtain an uniform martensite tissue (see, e.g., Japanese Patent Publication NO: 2008-546912).